Conductive polymers originally attracted the attention of researchers over 20 years ago. The interest generated by these polymers compared to conventional conducting materials (e.g., metals) was largely due to factors such as light weight, flexibility, durability, and potential ease of processing. To date the most commercially successful conductive polymers are the polyanilines and polythiophenes, which are marketed under a variety of tradenames.
The recent development of electroluminescent (EL) devices for use in light emissive displays has resulted in a rekindled interest in conductive polymers. EL devices such as organic light emitting diodes (OLEDs) containing conductive polymers generally have the following configuration:                anode/buffer layer/EL polymer/cathodeThe anode is typically any material that has the ability to inject holes into the otherwise filled π-band of the semiconducting, EL polymer, such as, for example, indium/tin oxide (ITO). In addition, conductive polymers can be used for the anode. The anode is optionally supported on a glass or plastic substrate. The EL polymer is typically a conjugated semiconducting polymer such as poly(paraphenylenevinylene) or polyfluorene. The cathode is typically any material, such as Ca or Ba, that has the ability to inject electrons into the otherwise empty π-band of the semiconducting, EL polymer.        
The buffer layer is typically a conductive polymer and facilitates the injection of holes from the anode into the EL polymer layer. The buffer layer can also be called a hole-injection layer, a hole transport layer, or may be characterized as part of a bilayer anode. Typical conductive polymers employed as buffer layers are the emeraldine salt form of polyaniline (PANI) or a polymeric dioxythiophene doped with a sulfonic acid. The most widely used dioxythiophene is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, abbreviated as PEDT/PSS. PEDT/PSS is available commercially from Bayer, as Baytron® P.
PEDT/PSS has emerged as a leading candidate for use as a buffer layer in EL devices such as red, green, blue organic light emitting diodes (RGB OLEDs). However, one factor which is inhibiting the widespread use of PEDT/PSS in RGB OLEDs is the inability to control conductivity of this material without sacrificing device performance. For example, in active matrix OLEDs, a buffer layer having higher conductivity can be useful. In passive matrix devices, a layer of PEDT/PSS having a conductivity no greater than the inherent conductivity of about 1.2×10−5 Siemens per centimeter (S/cm) is desired in order to minimize crosstalk between pixels in the display. It may be possible to decrease the conductivity by using very thin layers. However, reducing the thickness of PEDT/PSS buffer layers in OLEDs is not a good option, since thinner films give lower manufacturing yield due to the formation of electrical shorts. To avoid shorts, it is necessary to use a relatively thick buffer layer with a thickness of about 200 nm. It would be desirable to be able to form thicker layers of PEDT/PSS without increasing the conductivity.